Intravascular blood pump

ABSTRACT

An intravascular blood pump designed to be advanced through the blood vessel system of the patient, comprises a housing ( 15 ) accommodating an electric motor ( 12 ), the proximal end of the housing ( 15 ) being connected to a catheter ( 23 ) and the distal end thereof carrying a pump ( 11 ). The electric motor ( 12 ) includes a stator winding ( 17 ) forming a load-bearing component of the housing ( 15 ). The stator winding ( 17 ) is embedded in a matrix made of synthetic resin. The housing ( 15 ) is of an ironless design without any magnetic reflux device. The motor is operated with a rotational speed of about 50,000 upm. The magnetic stray field generated with such high frequencies does not disturb the cardiac rhythm of the patient. The motor can be given a compact size and thus has a high mechanical output power.

The invention relates to an intravascular blood pump comprising ahousing accommodating an electric motor, with the proximal end of thehousing being connected to a catheter and the distal end thereofcarrying a pump. An intravascular blood pump is a blood pump which canbe advanced through the vessel system of a patient so as to be operatedin the heart of the patient or at another site of the body.

From WO/44619, an intravascular blood pump is known which fulfills theabove conditions. This blood pump comprises a housing having a diameterof 7 mm at maximum and accommodating an electric motor arranged to drivethe impeller of a pump. The electric motor comprises a stator withinternal windings and external magnetic reflux metal-sheets. The refluxmetal-sheets are cast together with the stator winding in a housing madefrom plastic. The reflux metal-sheets function to concentrate themagnetic flow of the circulating magnetic field and to increase theefficiency of the electric motor by avoiding magnetic dissipationlosses.

DE 196 22 335 A1 describes a balloon catheter comprising a pump which isdriven by a motor arranged along the length of the catheter tube. Aguide channel for a guide wire is arranged to extend through thecatheter tube and coaxially through the pump. In this manner, theballoon catheter can be shifted together with the pump onto an alreadyset guide wire for positioning the pump at the desired site in thepatient's body.

U.S. Pat. No. 5,851,174 and EP 0 764 448 A2 each describe a cardiacsupport device comprising an intracardiac blood pump provided to beintroduced into the heart through an incision site. The blood pump hasan outer diameter of 9 to 12 mm. This fails to meet the demands posed toan intravascular blood pump. The motor comprises a stator, integratedinto the housing and having a stator winding, and a magnetic rotor. Therotor is provided with blades projecting into the annular space betweenthe stator and the rotor. For this reason, the annular space must have alarge width, causing the magnetic air gap between the rotor and thestator to become larger and reducing the performance of the motor andits efficiency, respectively.

An intravascular blood pump wherein the drive unit is integrated withthe pump member must have the smallest possible maximum outer diameterand a small rigid length. As of yet, no successful effort has been madeto design a blood pump suitable to operate with the required efficiencywhile having an outer diameter of less than 5 mm. An intravascular bloodpump is required to be capable of a delivery rate of 1.5 liters perminute for physiological pressures (60 to 80 mm Hg).

It is an object of the invention to provide an intravascular blood pumpwhich allows for a still further miniaturization so that the pump can beadvanced through the vessel system easily and safely.

According to the instant invention, the above object is achieved by thefeatures indicated in claim 1. A special characteristic of the bloodpump of the invention resides in that the stator of the electric motoris of an ironless design without any magnetic reflux device and that thestator winding is a structural component of the motor housing. Accordingto the invention, the structural component of the motor housing isformed by a stator winding embedded into a matrix made of syntheticresin. The current flowing in the stator winding generates a circulatingmagnetic field to be followed by the movement of the magnet deviceattached to the rotor. The omission of pole pieces and an ironcladreflux device will have the effect that the magnetic field generated inthe stator winding is not bundled externally of the stator winding, thuscausing dissipation losses towards the outside. Tests performed underspecial consideration of this effect have revealed that the magneticfield circulating at a high rotational speed does not have a detrimentalinfluence on the cardiac rhythm of the patient. The rotational speed ofthe magnetic field and thus also of the electric motor is in themagnitude of 50,000 rpm and will in any case be higher than 30,000 rpm.With such a high rotational speed, the rotating magnetic field has noharmful effects in the patient's body. In the blood pump of theinvention, the place for a reflux device is saved. Thus, the rotor canbe given a larger diameter, consequently allowing for an increase of themoment of rotation. Further, magnetic-reversal losses which would occurin a magnetic reflux device consisting of iron, are avoided. Thus, withthe above mentioned high rotational speeds, the increased dissipationlosses will be more than compensated for. Further, also the weight ofthe motor is reduced. The ironless design of the stator makes itpossible to use a larger wire thickness for the stator winding so thatthe current intensity can be increased while the ohmic losses in thestator winding will remain small.

In the blood pump of the invention, the housing containing the electricmotor can be reduced to an outer diameter of about 4 mm, whichcorresponds to a catheter of 12 F (F=French). The rigid axial length ofthe overall pump, i.e. of the motor housing and the pump unit, can bereduced to ≦20 mm. Thus, the intravascular blood pump can be advancedthrough the blood vessel system of the patient and be placed at thedesired site. The dimensions also make it possible to maneuver the bloodpump in an unobstructed and controlled manner through the arcus aortae.

The stator winding occupies at least 70%—preferably at least 80%—of thewall thickness of housing. The stator winding together with the resinousmatrix forms the load-bearing structural part of the housing wall.Generally, it will be sufficient to form the housing by the statorwinding in combination with the resinous matrix. It appears suitable,however, to provide the inner side of the housing wall with a protectiveinsulation layer which would also serve to protect the winding fromfriction and thus prevent the rotor from damaging the winding uponmechanical contact. Further, the outer side of the housing can beprovided with an additional protective foil, which foil must have goodheat-conducting properties to transfer the heat generated in the statorwinding to the blood flowing along on the outside.

For setting the blood pump together with the complementary catheter byuse of the Seldinger technique, the blood pump must comprise a guidechannel designed for passage of a guide wire therethrough. The bloodpump can then be advanced along the guide wire in the vessel system ofthe patient. The blood pump of the invention is suitably provided with aguide channel of the above type which is arranged to pass through theshaft of the rotor and through the axis of the impeller of the pump.Corresponding sealing elements can be provided to safeguard that bloodleaking into the guide channel will not enter into the catheter arrangedproximally of the housing, and intrude into the mechanics of the pump.

Embodiments of the invention will be explained in greater detailhereunder with reference to the drawings.

FIG. 1 is a longitudinal view of a first embodiment of the intravascularblood pump with a solid shaft,

FIG. 2 is a cross-sectional view through the housing wall, taken alongthe line II—II in FIG. 1,

FIG. 3 is a longitudinal view of a second embodiment of the blood pump,comprising a guide channel for a guide wire,

FIG. 4 is a view of a modification of the pump of FIG. 3 with a modifiedsealing arrangement for sealing the guide channel, and

FIG. 5 is a view of the sealing arrangement of FIG. 4 with a guide wireinserted therethrough.

The blood pump illustrated in FIG. 1 comprises a motor unit 10 and apump unit 11. The motor unit 10 comprises an electric motor 12 includinga stator 13 and a rotor 14. The stator 13 also forms the outer wall ofthe housing 15, i.e. there exists no additional housing surrounding thestator. The housing wall 16 forming the stator 13 comprises a statorwinding 17 made from wires embedded into a synthetic-resin matrix 18.The winding 17 is a so-called basket winding with wires extendingobliquely in the longitudinal direction of housing 15. Stator winding 17includes a plurality of coils, distributed along its periphery andconnected to each other in a star-shaped or triangular configuration,which are actuated successively to generate a circulating magneticfield. The sensor-free commutation of these coils is performed throughan extracorporeal control device connected to the motor by a multi-corewire line 24. Winding 17 is activated in a manner causing thecirculating magnetic field to rotate with a rotational speed of 50,000rpm.

Rotor 14 comprises a permanent magnet 20 mounted to shaft 19, with themagnet having its north pole N arranged on one side of its periphery andits south pole S on the other side of its periphery.

On the proximal end, shaft 19 is supported in a ball bearing 21. Theball bearing is held in a cap 22 arranged to close the proximal end ofhousing 15. The proximal end of housing 15 is joined by the catheter 23which comprises a flexible tube. Extending through the wall of catheter23 are the feed lines 24 for stator winding 17. In the presentembodiment, the housing cap 22 is connected to a projection member 25projecting into catheter 23 to obtain high mechanical stability.

The distal end of housing 15 is terminated by a transition piece 26which also includes a sealing 27 serving as a shaft bearing. Shaft 19extends through this sealing into pump unit 11 where the impeller 28 isattached to the distal end of the shaft. Impeller 28 rotates in thecylindrical pump housing 29 which is connected to housing 15 by at leastone web 30 arranged in the longitudinal direction. Pump unit 11 isdesigned for suctional intake of blood via the axial intake opening 31and for conveyance in the axial direction, the blood issuing laterallyfrom the openings 32 and flowing axially along housing 15 so that theflow heat is carried off from housing 15. Alternatively, the pump canalso be operated in the opposite sense.

In the embodiment according to FIG. 1, shaft 19 is a solid shaft. Therigid length of the overall blood pump along the motor unit and the pumpunit 11 is about 20 mm. The maximum outer diameter is 4 mm.

The wires of winding 17 embedded into the resinous matrix 18 of housingwall 16 without intermediate cavities are illustrated in FIG. 2. Thesewires are surrounded by an insulating sheath 33 a. The insulatingsheaths in turn are coated with stoving paint 33 b. After manufacture ofthe stator winding 17, the wires are bonded to each other whilesubjected to heat; in the process, the stoving paint layers of adjacentwires will be fused to each other and thus form a fixed wire structure.This wire structure, while placed in an injection mold, willsubsequently be enmolded by the synthetic resin 18 which is an epoxideresin. This compound comprising the winding and the epoxide resin is ofhigh mechanical stability so that the stoving paint 33 b servesexclusively for the preliminary fixation of the wires of the winding soas to facilitate the handling of the coil during the manufactureprocess. The stoving paint can be formed with correspondingly thinwalls, thus allowing to obtain an optimum relation between copper,stoving paint, insulation and epoxide resin. Notably, it is only thepercentage of the copper in the winding which is decisive for theefficiency of the motor.

After the housing 15 has been produced in the above manner, the catheter23 can be attached to the housing. Bearing 21 has an outer diametersmaller than the inner diameter of housing 15 and thus can be insertedinto the housing from the distal end.

The inner side of housing wall 16 is provided with a thin insulationlayer 34 of a captone foil (polyimide) having a strength of 12 to 25 μm.This insulating layer serves for insulating the wires and protectingthem from friction and thus preventing damage caused by the rotor, andfurther acts as a slide layer.

Arranged on the outer side of housing wall 16 is an cover foil 35 of amaterial with good heat conductivity, preferably of a metal such astitanium. By way of alternative to such a cover foil, the resinousmatrix 18 can be widened towards the outside.

The matrix 18 of synthetic resin comprises a duromer with a portion ofat least 50 percent by weight of Al₂O₃ to increase heat transfer to theoutside. The thickness of housing wall 16 inclusive of the layers 34 and35 is about 0,3 mm. The stator winding 17 occupies at least 70% andpreferably at least 80% of the wall thickness of housing wall 16.

The motor is of the toothless type, i.e. it is not provided withcircumferentially distributed pole pieces with windings held thereon.Instead, the stator winding is integrated into the wall of tubularhousing 15 and, in this region, considerably contributes to themechanical stability of housing wall 16.

The embodiment according to FIG. 3 is different from the firstembodiment in that the shaft 19 is formed as a hollow shaft and includesa guide channel 36 extending along the complete length of the shaft.Guide channel 36 communicates with the lumen of catheter 23 via afurther tube 40.

The distal end of shaft 19 is formed with an opening 37. Via thisopening, blood might leak into the guide channel 36. To keep this bloodfrom advancing into the interior of the electric motor, a sealing 38 isprovided proximally of bearing 21.

The blood pump according to FIG. 3 can be shifted over a guide wire (notshown) which extends through catheter 23 and guide channel 36 and isbeforehand placed in the patient's body. Except for this modification,the structural features and effects described in connection with thefirst embodiment apply also to the embodiment of FIG. 3.

The embodiment shown in FIGS. 4 and 5 likewise comprises a hollow shaft19 extending through the motor unit 10 and the pump unit 11 and forminga guide channel 36 for a guide wire. The proximal end of shaft 19 isjoined by a tube 40 passing through catheter 23, which tube is connectedto housing 15 and does not rotate along with shaft 19.

On the distal end of guide channel 36, a sealing 41 is provided forsealing the guide channel 36. This sealing 41 is a self-closing lipsealing. An opening is formed in the sealing for the passage of guidewire 42 therethrough. FIG. 5 does not illustrate the manner in which theguide wire 42 has pushed open the opening of sealing 41. Guide wire 42can thus be axially displaced within sealing 41. When withdrawn in theproximal direction, the guide wire will automatically close the sealing41.

A corresponding self-closing sealing 43 is arranged internally of shaft19. This sealing 43 is provided for additional sealing effect. The lumenof guide channel 36 has a diameter of 0.6 mm, thus allowing passagetherethrough of a guide wire of a corresponding diameter.

1. An intravascular blood pump comprising an elongate housingaccommodating an electric motor, the proximal end of the housing beingconnected to a catheter and the distal end thereof carrying a pump, theelectric motor comprising a stator winding, embedded in matrix made fromsynthetic resin, and a bladeless magnetic rotor supported for rotation,wherein the embedded stator winding exclusively forms a load-bearingcomponent of the housing, the housing being devoid of iron and of anymagnetic flux device.
 2. The blood pump of claim 1, wherein the housinghas a wall thickness and the stator winding occupies at least 70% of thewall thickness of housing.
 3. The blood pump of claim 2, wherein thewall thickness of the housing is smaller than 0.5 mm.
 4. The blood pumpof claim 1, characterized in that the electric motor comprises a hollowshaft and that the axis of the impeller of the pump is formed with aguide channel for a guide wire.
 5. The blood pump of claim 1, furthercomprising seals arranged at the distal end and the proximal end of thehousing between the housing and the shaft.
 6. The blood pump of claim 4,further comprising a seal arranged at the distal end of the housingbetween the housing and the shaft, and at least one further sealarranged in the course of the guide channel and allowing passage of theguide wire therethrough.
 7. The blood pump of claim 1, wherein the innerside of the housing has arranged thereon an insulating layer protectingthe stator winding.
 8. The blood pump of claim 1, wherein the outer sideof the housing has arranged thereon a cover layer protecting the statorwinding and providing for electric insulation and heat dissipation. 9.The blood pump of claim 1, wherein wires of the stator winding areprovided with an insulating sheathing surrounded by a stoving paintlayer.
 10. The blood pump of claim 4, wherein the proximal end of thehollow shaft is supported in a bearing having an outer diameter smallerthan the inner diameter of the stator.